Field of the Invention
The present invention relates to a thruster which is retractable into the hull of a floating or submersible vessel. The thruster is particularly advantageous for fitting to the stem or the bow of a boat or a ship.
The state of the art is constituted by numerous documents, and the most pertinent known to the Applicant are the following.
The Applicant's document EP-A-0 503 206 relates to a retractable or extendable thruster using a trapezoidal device that deforms on being pivoted, thereby generating rectilinear movement inside a well. The thruster is retractable or extendable and is made up of a box fixed in leakproof manner via joint planes to a well that is an integral portion of the structure of the vessel. Two asymmetric pivot arms are folded inside the box, together with a motor-driven base unit, a bracket, and a helical assembly. The two arms are hinged firstly to the box and secondly to the bracket which is secured to the thrust base unit. Under manual or mechanical drive exerted on a lever secured to one of the arms by the shaft, said atm pivots together with the other or "triangulation" arm and controls deformation of the trapezium, thereby obtaining rectilinear movement of the base at the center thereof.
Although technically most effective, the cost of manufacturing such a thruster is prohibitive.
The number of moving parts and the design of the linkage they form increase the sale price of the thruster considerably.
Document FR-A-2 229 608 proposes a motor, e.g. a hydraulic motor, which drives a vertical or sloping shaft having two pieces capable of sliding one relative to the other. The lower portion of the shaft drives a propeller via angle gearing. Because of the slidable drive shaft, the propeller can be retracted and raised above the waterline. This sliding can be driven by a hydraulic actuator controlled with the same oil under pressure as drives the hydraulic motor. The propeller may be steerable to steer the boat. In its high position, retracted into a well provided for this purpose, the raisable portion can close said well so as to restore full hydrodynamic performance to the hull of the boat.
The essential problem with that device lies in the fact that the thruster is steerable. In the most advantageous embodiment, that kind of thruster is used for moving the stem of a ship substantially perpendicularly to the longitudinal axis of the ship. Since such movement is always along the same direction, the steering angle must be constant. In addition, having a steerable thruster increases the financial costs associated with designing and building that type of device, and therefore increases the sale cost thereof.
Document FR-A-2 348 850 deals with a device for locking a retractable thruster for a boat: locking takes place by means of four hinged and inclined latches producing thrust with both vertical and horizontal components, and four hinged latches producing horizontal thrust. The invention applies to large thrusters that are vertically retractable into a very large housing in a boat, which housing receives a moving box carrying the thruster assembly, with the thrust forces therefrom being transmitted to the boat by the entire structure for guiding the box. That device for locking a boat thruster acts both vertically and horizontally. Its structure is complex and therefore expensive, with four latches hating orientations that are specific, thus requiring the latches to be capable of withstanding thrust forces.